Tool Steel D2 vs M2: Cold Work vs High-Speed Cutting

## Classification **D2** is a Group D (cold-work, high-carbon high-chromium) tool steel. Air-hardening and dimensionally stable, designed for room-temperature tooling. **M2** is a Group M (molybdenum high-speed) tool steel. Designed to maintain hardness at temperatures up to 600 degrees C during high-speed cutting. ## Composition | Element | D2 (UNS T30402) | M2 (UNS T11302) | |---------|-----------------|------------------| | Carbon | 1.40-1.60% | 0.78-0.88% | | Chromium | 11.0-13.0% | 3.75-4.50% | | Molybdenum | 0.70-1.20% | 4.50-5.50% | | Tungsten | None | 5.50-6.75% | | Vanadium | 0.50-1.10% | 1.75-2.20% | ## Heat Treatment and Hot Hardness | Property | D2 | M2 | |----------|-----|-----| | Working Hardness | 58-62 HRC | 63-66 HRC | | Hot Hardness at 600C | ~40 HRC | ~58 HRC | M2 retains hardness at elevated temperatures. At 600 degrees C, M2 still measures approximately 58 HRC while D2 has dropped to approximately 40 HRC. ## Toughness D2 has better toughness than M2. For stamping and blanking dies that experience shock loading, D2's toughness advantage is critical. M2 is relatively brittle and can chip under interrupted cuts. ## Cost D2 costs approximately 4-6 USD/kg. M2 costs approximately 8-15 USD/kg, reflecting its higher alloy content. ## When to Choose Each **Choose D2 when**: The tool operates at ambient temperature, the primary failure mode is abrasive wear, and some impact loading occurs. Key applications include blanking dies, stamping dies, slitter knives, and cold-forming punches. **Choose M2 when**: The tool must cut metal at high speeds, hot hardness is essential, and the application is a cutting tool. Key applications include twist drills, end mills, taps, milling cutters, and saw blades.